Use of barium metaborate in electrodepositable compositions

ABSTRACT

THIS INVENTION RELATES TO NOVEL PIGMENTED ELECTRODEPOSITABLE COMPOSITIONS. MORE PARTICULARLY, THIS INVENTION RELATES TO THE USE OF BARIUM METABORATES TO REDUCE STAIN OF RESIN FILMS ELECTRODEPOSITED ON IRON CONTAINING METAL SUBSTRATES, PARTICULARLY STEEL SUBSTRATES.

United States Patent O 3,645,871 USE OF BARIUM METABORATE IN ELECTRO-DEPOSITABLE COMPOSITIONS Myron J. Krupp, Grafton, Frederick R. Colburn,Franklin, and John P. Knudtson, Milwaukee, Wis, assignors to PPGIndustries, Inc., Pittsburgh, Pa. No Drawing. Filed Aug. 8, 1968, Ser.No. 751,033 Int. Cl. C23b 13/00 US. Cl. 204-181 7 Claims ABSTRACT OF THEDISCLOSURE This invention relates to novel pigmented electrodepositablecompositions. More particularly, this invention relates to the use ofbarium metaborates to reduce stain of resin films electrodeposited oniron containing metal substrates, particularly steel substrates.

Recently, electrodeposition has been achieving wide industrialacceptance as a method of applying protective coatings. The coatingsachieved have excellent properties for many applications andelectrodeposition results in a coating which does not run or Wash offduring baking. Virtually any conductive substrate may be coated byelectrodeposition. The most commonly employed substrates include thebase metals such as iron, steel, aluminum, copper, zinc, brass, tin,nickel and chromium, as Well as other metals and pretreated metals.Impregnated paper, or other substrates rendered conductive under theconditions employed, may also be coated.

Electrodeposition of certain materials, including waxes, natural andsynthetic resins, have been known in the art for some time. Likewise, arecent US. Pat. No. 3,23 0,162, describes a method and compositionspresently utilized in the field of automotive finishing and industrialcoatings.

While electrodeposition is in many respects advantageous compared toordinary application methods, problems have arisen in the fact that theelectrodeposition of synthetic polycarboxylic acid resin vehicles ontoironcontaining substrates such as steel frequently produces stainedcoatings. This staining is a particular problem in pigmented coating andespecially in white, pastel or other light color pigmented films. It hasnow been found that the use of barium metaborate in pigmentary form whenpresent in pigmented electrodepositable coating compositions greatlyreduces the tendency of staining, either locally or as an overall yellowtone contribution. This is especially true in white coatings Wherewhiter whites are produced in comparison to compositions without bariummetaborate. The improvement is significant for reflectance as well asesthetic qualities.

The presently preferred synthetic polycarboxylic acid resin employed inthe compositions of the invention are acrylic interpolymers whichcontain from about one percent to about 20 percent by weight of ahydroxyalkyl ester of acrylic acid, methacrylic acid, or other,alpha,betaethylenically unsaturated carboxylic acid. These esters may beformed from an alkylene glycol esterified with the acid, or they can beproduced by reaction of the acid with an alkylene oxide.Interpolymerized with the hydroxyalkyl ester is from about one percentto about 20 percent by weight of an unsaturated carboxylic acid, and atleast one other ethylenically unsaturated monomer copolymerizable withthe acid and the ester.

The preferred hydroxyalkyl esters in the acrylic interpolymer are estersof acrylic acid and methacrylic acid in which the hydroxyalkyl group hasup to about carbon atoms, such as 2-hydroxyethyl acrylate,2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, Z-hydroxyethylmethacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl 3,645,871Patented Feb. 29, 1972 methacrylate, 4-hydroxybutyl methacrylate, andmixtures of such esters. Corresponding esters of other unsaturatedacids, for example, ethacrylic acid, crotonic acid, and similar acids ofup to about 6 carbon atoms, can also be employed.

In addition to esters of unsaturated monocarboxylic acids, there may beemployed monoor diesters of unsaturated dicarboxylic acids, such asmaleic acid, fumaric acid, and itaconic acid, in which at least one ofthe esterifying groups contains a hydroxyl group. Such esters ofunsaturated dicarboxylic acids provided specific characteristics incertain compositions. Examples of such esters include monoZ-hydroxyethyl maleate, mono Z-hydroxyethyl) fumatate, bis(2-hydroxyethy1) maleate, mono Z-hydroxypropyl) maleate, bis2-hydroxypropyl) maleate, mono 2-hydroxyethyl itaconate, bis(Z-hydroxyethyl itaconate, and 2-hydroxyethylbutyl maleate.

The unsaturated acid monomer of the interpolymer is preferably acrylicacid or methacrylic acid, although other acids of up to about 6 carbonatoms, such as the unsaturated monocarboxylic acids and dicarboxylicacids described above in connection with the esters, can also beutilized. When a monoester of a dicarboxylic acid is utilized as thehydroxyalkyl monomer, it may also be considered as all or part of theacid monomer.

While the acrylic interpolymers of the above may be utilized as a solefilm-forming ingredient, they are normally used in conjunction with upto 50 percent by Weight of an amine-aldehyde condensation product.Examples of such amine-aldehyde condensation products employed arealdehyde condensation products of melamine, urea, acetoguanamine or asimilar compound, and may be watersoluble or organic solvent soluble.Generally, the aldehyde employed is formaldehyde, although usefulproducts can be made from other aldehydes such as acetaldehyde,crotonaldehyde, acrolein, benzaldehyde, furfural and others.Condensation products of melamine or urea are the most common and arepreferred,but products of other amines and amides in which at least oneamido group is present can be employed.

For example, such condensation products can be produced with triazines,diazines, triazoles, guanadienes, guanamines, and alkyl-andaryl-substituted cyclic ureas, and alkyland aryl-substituted melamines.Examples of such compounds are:

N,N'-dimethyl urea Benzyl urea N,N-ethylene urea Diazine diamideFormaguanamine Benzoguanamine Ammeline2-chloro-4,6-diamino-1,3,5-triazine 3,5-diaminotriazole4,6-diarninopyrimidine 2,4,6-triphenyltriamino-1,3,5-triazine and thelike.

These aldehyde condensation products contain methylol groups or similaralkylol groups, depending upon the particular aldehyde employed. Ifdesired, these methylol groups can be etherified by reaction with analcohol. Various alcohols are employed for this purpose, includingessentially any monohydric alcohol, although the preferred alcohols aremethanol, butanol, and similar lower alkanols.

The amine-aldehyde condensation products are produced in a mannerwell-known in the art, using acidic or basic catalysts and varyingconditions of time and temperature. The aldehyde is often employed as asolution in water or alcohol, and the condensation, polymerization andetherification reactions may be carried outeither sequentially orsimultaneously.

Electrodeposition compositions comprising the above interpolymers and anamine-aldehyde resin are more fully described in copending applicationSer. No. 368,394, filed May 18, 1964, now US. Pat. 3,403,088.

In order to produce an electrodepositable composition, it is necessaryto at least partially neutralize the acid groups present with a base inorder to disperse the resin in the electrodeposition bath. Inorganicbases such as metal hydroxides can be used, but it is preferred to useammonia or organic bases, especially water-soluble amines, such as, forexample, the mono-, diand tri-lower alkyl amines such as propylamine,butylamine, dimethylamine, diethylamine, dipropylamine,diisopropylamine, dibutylamine and m-methylbutylamine, triethylamine,tributylamine, methyldiethylamine, dimethylbutylamine, and the like;cyclic amines such as morpholine, pyrrolidine, piperidine; diamines suchas hydrazine, methylhydrazine, 2,3- toluene diamine, ethyl diamine andpiperizine and substituted amines such as hydroxylamine, ethanolamine,diethanolamine, butanolamine, hexanolamine and methyldiethanolamine;octanolamine, diglycolamine and other polyglycol amines,triethanolamine, and methylethanolamine, n-amino-ethanolamine andmethyldiethanolamine and polyamines such as diethylene triamine,triethylene tetrarnine, and hexamethylene tetramine.

The barium metaborate is introduced into the compositions of theinvention in the same manner as convention-a1 pigments are dispersed.Preferably, the barium metaborate is reduced to a small particle size,usually less than about 200 mesh and, preferably, less than about 25microns and, more preferably, below microns before being added to thevehicle. If large particles of barium metaborate are introduced, thegrinding will require more time and perhaps a filtration step to removeoversized particles remaining.

The barium metaborate is dispersed by grinding in the presence of atleast a portion of the vehicle resin and, in most cases, a surfactant ordispersing agent, or in surfactant or dispersing agent with lateraddition of a vehicle resin. Grinding is accomplished by the use of ballmills, sand mills, Cowles dissolvers, continuous attritors, and thelike, until the pigment has been reduced to the desired size, and,preferably, has been wet by and dispersed in the vehicle resin and/ordispersing agent.

Preferably, the grinding is conducted in an aqueous dispersion ofneutralized resin having a pH above about 7 and preferably about 9.0.The amount of water present in such an aqueous grind is not critical;however, commonly the resin employed in the grinding step is about 30 to70 percent solids. The use of more water merely reduces the effectivecapacity of the mill and, while less water can be employed, theviscosity creates some problems in certain instances.

The pigment-binder ratio in the grinding step is not critical; however,levels between about 3.5/1 to 7/1 are frequently employed, althoughother levels may be utilized.

After grinding, the particle size should be in the range of 10 micronsor less, preferably as small as practicable. Generally a Hegman grindgauge reading of about 6 is the minimum for a presentlycommercially-acceptable composition.

For a general review of pigment grinding and paint formulation,reference may be had to: D. H. Parker, Principles of Surface CoatingTechnology, Interscience Publishers, New York (1965); R. L. Yates,Electropaint ing, Robert Draper Ltd., Teddington, England (1966);

4 and H. F. Payne, Organic Coating Technology, vol. II, Wiley & Sons,New York (1961).

The pigments present may be any of the pigments conventionallyemployedin the art. Since the staining phenomena previously described is mostnoticeable in white compositions and the improvement is likewise mostmarked, the invention is particularly useful in white coatings, that is,coatings containing white pigment. Generally titanium dioxide is thesole or chief white pigments; other white pigments and/or extenderpigments include, antimony oxide, zinc oxide, basic lead carbonate,basic lead sulfate, barium carbonate, chin-a clay, calcium carbonate,aluminum silica, silica, magnesium carbonate, magnesium silica, amongothers. Color pigments may also be employed, for example, cadmiumyellow, cadmium red, carbon black, phthalocyanine blue, chrome yellow,toluidine red, hydrated iron oxide, among others.

The amount of barium metaborate employed is not critical; anysignificant amount will demonstrate some effect. Generally the amount ofbarium metaborate employed may be expressed as a percentage of totalpigment present. Generally barium metaborate is employed in amountsranging from 0.5 to about 10 percent, based on total pigment. Largeramounts may be employed, but generally do not give commensurateimprovement and thus are usually unnecessary. Preferably bariummetaborate is employed in amounts of about 1 percent to about 5 percentof the total pigment present.

There is often incorporated into the pigment composition a dispersing orsurface active agent. If such a surface active agent is used, it shouldbe the non-ionic or anionic type or a combination of these types. It isdesirable to avoid the use of any cationic type agent. Usually thepigment and surface active agent, if any, are ground together in aportion of the vehicle, or alone, to make a paste and this is blendedwith the vehicle to produce a coating composition.

It has been found especially important to regulate the ratio of pigmentto the vehicle in compositions which are used in electrodepositionprocesses. In most instances the most desirable coatings are obtainedwhen the coating composition contains a ratio of pigment-to-vehicle ofnot higher than 2 to 1. If the composition has too high apigment-to-vehicle ratio, the electrodeposited films may exhibit verypoor flow characteristics and, in many instances, are noncontinuous andhave poor film appearance.

In many instances, it is preferred to add to the bath in order to aiddispersibility, viscosity and/or film quality, a non-ionic modifier orsolvent. Examples of such materials are aliphatic naphthanic or aromatichydrocarbons or mixtures of the same; monoand dialkyl ethers of glycols,pine oil and other solvents compatible with the resin system. Thepresently preferred modifier is 4-rnethoxy-4-methylpentanone-2(Pent-Oxone).

There may also be included in the coating composition, if desired,additives such as antioxidants. For example, orthoamylphenol or cresol.It is especially advantageous to include such antioxidants in coatingcompositions which are used in baths which may be exposed to atmosphericoxygen at elevated temperatures and with agitation over extended periodsof time.

Other additives which may be included in coating compositions, ifdesired, include, for example, wetting agents such as petroleumsulfonates, sulfated fatty amines, or their amides, esters of sodiumisothionates, alkyl phenoxypolyoxyethylene alkanols, or phosphate estersincluding ethoxylated alkylphenol phosphates. Other additives which maybe employed include anti-foaming agents, suspending agents,bactericides, and the like.

In formulating the coating composition, ordinary tap water may beemployed. However, such water may contain a relatively high level ofmetals and cations which, while not rendering the process inoperative,may result in variations of properties of the baths when used inelectrodeposition. Thus, in common practice, deionized water, i.e.,water from which free ions have been removed by the passage through ionexchange resins, is invariably used to make up coating compositions ofthe instant invention.

In the electrodeposition process, a process well-described in the art,the aqueous bath containing the composition is placed in contact with anelectrically-conductive anode, and an electrically-conductive cathode.The coating is deposited upon the anode so that the metal substrate tobe coated is used as the anode. Upon passage of electric current(normally direct current) between the anode and the cathode while incontact with the bath containing the coating composition, an inherentfilm of the coating composition is deposited on the anode.

The conditions at which the electrodeposition process is carried out arethose conventionally used in electrodeposition. The applied voltage mayvary greatly and can be as low as, for example, 1 volt or as high, forexample, as 500 volts or higher. It is typically between 50 and 350volts. The current tends to decrease during electrodeposition and thefilms become electrically insulative and cause the deposition of film tobe self-terminating at any particular voltage.

The anode being coated may be any iron-containing metallic substrate,generally the substrate is steel. Usually the steel employed isgalvanized or chemically pretreated, for example, with zinc phosphate,iron phosphate, calcium-zinc phosphate or other metal pretreatment toimprove corrosion resistance.

The concentrations of the coating composition in the aqueous bath usedin electrodeposition is not critical and relatively high levels ofcoating composition can be used; however, it is ordinarily desirable touse a low concentration of coating composition since this is one of thebenefits inherent in the system. Baths containing as little as onepercent by Weight of the coating composition in water can be employed.In general practice, the baths used usually contain between 5 and aboutpercent by weight of paint solids. Generally, it is preferred not to usemore than or percent by weight of the coating composition in the bath,although there is no technical reason why films cannot be produced ineven higher levels. Once the film is deposited upon the substrate andthe substrate removed from the bath, the article is treated as one whichhas been coated in the conventional painting operation. The article maybe air-dried, or, usually, it is heated in an oven or by some otherappropriate means to bake or dry the film. When this is done, the bakingtemperatures of about 275 F. to about 375 F. for 60 to 10 minutes areusually employed.

The invention is further described in conjunction with the followingexamples, which are to be considered illustrative rather than limiting.All parts and percentages in the examples and throughout thisspecification are by weight unless otherwise stated.

EXAMPLE I Parts by wt. Vehicle resin I (above) 4418 Dimethylethanolamine3.7 Deionized water 79.0 TiO 123.0 SiO 8.5 Barium metaborate 2.4 Zincoxide 1.35

The sand mill was washed out with 10 parts of deionized water. This isdesignated Pigment Paste I.

The following composition was formed and then blended with Pigment PasteI:

Parts by wt.

Vehicle resin I 231.0

Diisopropanol amine 24.2 Ethylated methylated hexamethylmelamine (XMDeionized water 362.4

The pH of the final composition was 8.65.

The above composition was reduced to 10 percent solids and electrocoatedon a calcium-zinc phosphate treated steel panel for seconds at 250 voltsto deposit .90 mil. The panel was pre-immersed at a bath temperature of82 F. The initial amperage 'was 2.8, the final amperage .20. Whencompared to a control coating deposited under similar conditions, withthe exception that the barium metaborate was removed from the formula,the coating of the invention produced a noticably whiter white whichcould be measured as a two percent difference on the axis of acolor-eye. In addition to the above difference, the panel of theinvention demonstrated improved salt spray resistance over the control.

According to the provisions of the patent statutes, there are describedabove the invention and what are now considered its best embodiments;however, within the scope of the appended claims, it is to be understoodthat the invention can be practiced otherwise than is specificallydescribed.

What is claimed is:

1. A method of coating a metal substrate which comprises passingelectric current between an electrically conductive metal anodecontaining iron and an electrically conductive cathode in contact with awater-dispersed coating composition comprising:

(a) An at least partially-neutralized interpolymer of from about onepercent to about 20 percent by weight of a hydroxyalkyl ester of analpha, beta-ethylenically unsaturated carboxylic acid, from about one toabout 20 percent by weight of an unsaturated carboxylic acid and atleast one other copolymerizable ethylenically unsaturated monomer;

(b) a pigment; and

(c) barium metaborate.

2. A method as in claim 1 wherein the anode comprises steel.

3. A method as in claim 2 wherein the pigment (b) comprises titaniumdioxide.

4. A method as in claim 2 wherein the water-dispersed coatingcomposition comprises:

(a) from about percent to about 50 percent by weight, based on the totalof (a) and (b) herein, of an at least partially-neutralized interpolymerof from about one percent to about 20 percent by weight of ahydroxyalkyl ester of an alpha, beta-ethylem'cally unsaturatedcarboxylic acid, from about one percent to about 20 percent by weight ofan unsaturated carboxylic acid, and at least one other copolymerizableethylenically unsaturated monomer;

(b) from about 5 percent to about 50 percent by weight of at least onemember of the group consisting of an aminealdehyde condensation productand a polyepoxide;

(c) a pigment; and

(d) barium metaborate.

5. A method as in claim 3 wherein the pigment (c) comprises titaniumdioxide.

6. A method as in claim 2 wherein the water-dispersed compositioncomprises:

(a) from about 95 percent to about 50 percent by weight, based on thetotal of (a) and (b) herein, of an at least partially-neutralizedinterpolymer of from about one percent to about 20 percent by weight ofa hydroxyalkyl ester of an alpha, beta-ethylenically unsaturatedcarboxylic acid of up to about 6 carbon atoms, said ester having fromabout 2 to about'5 carbon atoms in the hydroxyalkyl group; from aboutone percent to about 20 percent by Weight of an unsaturated carboxylicacid of up to about 6 carbon atoms; and at least one othercopolymerizable ethylenically unsaturated monomer;

(b) from about 5 percent to about 50 percent by weight of a condensationproduct of formaldehyde and a member of the group consisting ofmelamine, urea, guanamine, and substituted derivatives thereof;

(0) a pigment; and

(d) barium metaborate.

7. A method as in claim 6 wherein the pigment (c) is titanium dioxide.

References Cited UNITED STATES PATENTS 3,175,964 3/1965 Watanabe et al.204-181 X 5 3,230,162 1/1966 Gilchrist 204--l81 3,290,235 12/1966Gilchrist 204181 3,378,477 4/1968 Gentles et a1 204181 3,403,088 9/1968Hart 204181 OTHER REFERENCES 10 Ross et al., Modified Barium MetaboratePigments For Alkyd Paints, Paint Tech., 31, No. 4, pages 14, 16 and 20most pertinent, April 1967.

PATRICK P. GARVIN, Primary Examiner l5 U .5. C1. X.R.

